1. Field of the Invention
The present invention relates to a method of inspecting a mask pattern, an inspection apparatus, inspecting data used therein and a method of generating the inspecting data, and more particularly to the extraction and inspection of inspecting accuracy data in a process for inspecting a photomask.
2. Description of the Related Art
In recent years, a semiconductor integrated circuit device (hereinafter referred to as an LSI) in each product is evaluated as a key device, and an increase in the scale and speed of the LSI has been required in order to maintain the competitiveness of the product. A fine process is necessary with the microfabrication of an element and an increase in integration.
Under the circumstances, process conditions have been increasingly restricted in order to form a pattern as designed.
In the formation of the semiconductor integrated circuit device, an isolation is carried out over, the surface of a semiconductor substrate and a well having a desirable concentration is formed, and an impurity diffusion region having a desirable conductivity type is formed in the well, and furthermore, an insulating film is formed and a wiring pattern is provided.
For example, in the formation of the wiring pattern, a photolithographic step of forming a conductive film such as a polycrystalline silicon layer, an aluminum layer or a metal silicide layer and then carrying out exposure through a photomask to form a desirable mask pattern is carried out, and etching is performed by using the mask pattern as a mask, thereby forming the wiring pattern.
At the etching step, the conductive film exposed from the mask pattern is selectively removed. Even if various conditions such as the concentration and temperature of an etchant are optimized, an etching speed is varied depending on the density (area ratio) of the mask pattern, and further more, the peripheral length of the mask pattern. For this reason, accuracy in etching is varied depending on the density of the mask pattern or a pattern pitch. Even if a mask pattern region is excessively large or small, the accuracy in the etching is reduced.
Moreover, the formation of a diffusion layer also has the same problems. If an ion implantation region for forming the diffusion layer is too small, the concentration of the ion is generated so that a desirable diffusion profile cannot be obtained. Accordingly, the accuracy in the photomask for forming the mask pattern for diffusion is also very important.
In each process, a pattern is formed by using the photomask. The pattern accuracy of the mask pattern on the photomask greatly depends on the accuracy in the pattern formation in the process. Therefore, a demand for an enhancement in the accuracy has been increased.
Under the circumstances, at a defect inspecting step, necessary accuracy for a region which is to have the highest accuracy in a photomask to be inspected is acquired from a photomask designer and an inspection is carried out by using a value thereof as a reference value. Thus, an effort to reduce the defect of the photomask has been made.
For this reason, over one photomask, all regions are inspected based on the same inspection reference. Therefore, a defect set within such a range as not to originally influence an actual circuit operation is treated to be present, and correction or manufacture is carried out again. Consequently, there is a problem in that a time (TAT) required from an order to a completion is increased.
Moreover, the photomask is expensive. Therefore, a sudden rise in a cost caused by the necessity of a large number of photomask blanks for carrying out the manufacture again is also a serious problem.
In a recent process for manufacturing a semiconductor integrated circuit, moreover, there has been proposed a method of CMP (Chemical Mechanical Etching) for flattening the surface of a substrate. For example, this method serves to form an insulating film on a surface by a coating method of a CVD method and to then carry out chemical etching while performing mechanical polishing, thereby flattening the surface. In the case in which the pattern density of a wiring layer to be a lower layer is low and there is a region including a pattern having a predetermined area or less, however, the flattening cannot be carried out even if the insulating film is formed thickly. As a result, a region having no wiring pattern after the CMP becomes a concave portion so that a dent state is maintained.
In the case in which the layout pattern has a deviation, thus, sufficient pattern accuracy for the layer cannot be obtained. In addition, there is a problem in that the pattern accuracy of an upper layer is also influenced. Consequently, there is a problem in that the process accuracy cannot be sufficiently obtained.
Therefore, it is conceived to extract the area ratio of the mask pattern from the layout pattern of a semiconductor chip, additionally providing a dummy pattern to the layout pattern to adapt the area ratio of the mask pattern of a layer constituting the layout pattern in consideration of the optimum area ratio of the layout pattern of the layer obtained based on the process conditions of the layer, thereby setting the layer to have the optimum area ratio.
A photomask to be a very important element in such an increase in accuracy in a pattern is used through a defect inspecting step.
Also in the inspection, necessary accuracy in a portion in which the toughest accuracy conditions in the photomask to be inspected is acquired from the designer of the photomask and the inspection is carried out by using the data.
According to this method, it is possible to advance the inspection without specifying a place having the toughest portion in the creation and inspection of the photomask. Thus, a yield can be enhanced.
Description will be given to a conventional photomask inspecting flow with reference to the drawings.
FIG. 25 is a flow chart showing a conventional photomask inspection.
In this method, first of all, the pattern of a photomask is created based on a design rule (step 101). Next, the pattern of the photomask thus obtained is converted into data for photomask drawing and data are transferred to the manufacturing division of the photomask or another manufacturing company thereof so that a photomask is started to be actually manufactured (step 102).
The minimum value of the design rule of a pattern is specified as inspection accuracy data when the data are thus transferred (step 106).
On the other hand, the photomask manufacturing division or another manufacturing company thereof draws a pattern on a photomask blank by using the drawing data of the photomask formed at the step 102, thereby forming the photomask (step 103).
Next, the result of the pattern formation is decided based on the inspecting accuracy data obtained at the step 106 (step 104).
Then, it is decided that only the pattern formation decided to be within the range of the inspecting accuracy data is acceptable (step 105).
With the recent microfabrication of a process, however, a minimum pattern width and a minimum interval tend to be increasingly reduced. For example, consideration will be given to the case in which there is formed a photomask including patterns 210 to 213 having a minimum width which is arranged at a minimum interval 203 as shown in FIG. 26A and patterns 214 to 216 provided at a large interval 204 as shown in FIG. 26B. For example, it is assumed that the tolerance of a defect formed in a pattern having the minimum interval 203 is set to have a size represented by an allowable defect 201. At this time, in the case in which a pattern defect 206 having a smaller size than the size of the defect 201, it is decided that this is the tolerance at the inspecting step.
In the case in which there is a pattern defect 202 having a greater size than the size of the allowable defect 201, moreover, it is decided that the photomask is a defect in the inspection because the defect 202 is larger than the allowable defect 201 at the inspecting step.
However, the allowable defect 201 has one size in the same photomask and the same processing is carried out based on the allowable defect 201 in any region having a great pattern width.
For this reason, in the case in which there is the pattern defect 202 having a greater size than the size of the allowable defect 201, the interval 204 is much greater than the minimum interval 203 as shown in FIG. 26B. Therefore, it is decided that the defect 202 is also a defect at the inspecting step between the patterns 214 and 215. Even if such a defect is thus present in the region having a great interval in an actual design rule, however, there is no problem. In spite of the foregoing, a correcting step is started so that a step of carrying out an inspection again is added.
In the conventional method, thus, a demand for inspecting accuracy corresponding to the minimum interval 203 is given over the whole photomask. Therefore, it is decided that the defect 202 having such a size as not to make troubles is also a defect at the inspecting step.
Also in the case in which the same defect is generated and patterns might be actually short-circuited with each other, there is no problem when an adjacent pattern has the same node or a dummy pattern is formed for the purpose. Accordingly, it is not necessary to carry out the correction. However, the same defect is decided to be a defect in this case, the correcting step is started and the step of carrying out the inspection again is added.
Therefore, the inspection is executed with unnecessary accuracy so that a correction frequency is increased. Consequently, there is an obvious problem in that a reduction in a photomask creating period (TAT) and a decrease in the cost of creation are hindered.